Field of the Invention
The present invention relates to a damping force variable valve assembly installed in a damping force variable shock absorber, and a damping force variable shock absorber including the same, and more particularly, to a damping force variable valve assembly that maintains a damping force at a medium level by maintaining a position of a spool at a fail position upon fail of a solenoid installed in a damping force variable valve, thereby providing satisfactory steering performance and ride comfort, and a damping force variable shock absorber including the damping force variable valve assembly.
Description of the Related Art
In general, a shock absorber is installed in means of transportation, such as automobile or the like, and improves ride comfort by absorbing and damping a vibration or shock from a road surface during driving, or improves ride comfort by maintaining a posture of a vehicle body so as to be resistant to a force such as an inertial force applied to the vehicle body during driving.
Such a shock absorber includes a cylinder and a piston rod installed to be compressible and extendable within the cylinder. The cylinder and the piston rod are connected to a vehicle body, wheels, or axles.
A shock absorber, a damping force of which is set to be low, can improve ride comfort by absorbing a vibration caused by unevenness of a road surface during driving. On the contrary, a shock absorber, a damping force of which is set to be high, can improve steering stability by suppressing a change in a posture of a vehicle body. Therefore, in a conventional vehicle, a shock absorber, to which damping force characteristics are differently set according to the purpose of use of the vehicle, is selected.
Meanwhile, a damping force variable shock absorber has been recently developed, which is equipped with a damping force variable valve at one side thereof so as to appropriately adjust damping force characteristics thereof for the purpose of improving ride comfort or steering stability according to a road surface, a driving condition, and the like.
FIG. 1 is a sectional view illustrating an example of a damping force variable shock absorber according to the related art. Referring to FIG. 1, the damping force variable shock absorber 10 according to the related art includes a base shell 12, and an inner tube 14 which is installed inside the base shell 12 and in which a piston rod 24 is movably installed in a length direction. A rod guide 26 and a body valve 27 are installed in an upper portion and a lower portion of the inner tube 14 and the base shell 12, respectively. In the inside of the inner tube 14, a piston valve 25 is connected to one end of the piston rod 24, and the piston valve 25 partitions the inner space of the inner tube 14 into a rebound chamber 20 and a compression chamber 22. A top cap 28 and a base cap 29 are installed in an upper portion and a lower portion of the base shell 12, respectively.
A reservoir chamber 30 is formed between the inner tube 14 and the base shell 12 to compensate for a change in the volume of the inner tube 14 according to the reciprocating motion of the piston rod 24. A flow of a working fluid between the reservoir chamber 30 and the compression chamber 22 is controlled by the body valve 27.
In addition, a separator tube 16 is installed inside the base shell 12. The inside of the base shell 12 is partitioned by the separator tube 16 into a high-pressure chamber PH connected to the rebound chamber 20, and a low-pressure chamber PL serving as the reservoir chamber 30.
The high-pressure chamber PH is connected to the rebound chamber 20 through an inner hole 14a of the inner tube 14. The low-pressure chamber PL is connected to the compression chamber 22 through a lower passage 32 formed between a body of the body valve 27 and the base shell 12 (or the base cap 29) and a passage formed in the body valve 27.
Meanwhile, the shock absorber 10 according to the related art includes a damping force variable valve assembly 40 mounted on one side of the base shell 12 so as to vary a damping force.
The damping force variable valve assembly 40 is provided with passages respectively connected to the base shell 12 and the separator tube 16 and communicating with the high-pressure chamber PH and the low-pressure chamber PL. In addition, the damping force variable valve assembly 40 includes a spool 44 installed to be moved by a driving of a plunger 42. An inner passage communicating with the high-pressure chamber PH and the low-pressure chamber PL is varied by the movement of the spool 44, and the damping force of the shock absorber is varied accordingly. The plunger 42 is configured to move in a left-right direction, when viewed in FIG. 1, due to a magnetic force generated when an electric current flows through a solenoid.
In the damping force variable valve assembly according to the related art, for example, when the plunger 42 moves left, the spool 44 closes the passage to generate a high damping force (hard mode). On the contrary, when the plunger 42 moves right, the spool 44 opens the passage to generate a low damping force (soft mode).
However, in the damping force variable shock absorber according to the related art, if the supply of the electric current to the solenoid is stopped (that is, failed) due to an accident such as a disconnection of a power line or the like, the spool and the plunger are positioned such that the damping force variable valve assembly implements only one of the soft mode and the hard mode. Due to this, the damping force variable shock absorber according to the related art is subjected to deterioration in the steering performance and the behavior stability of the vehicle causing safety problems, or to an unpleasant ride comfort due to an excessive damping force.